Examples Collapse

Collapse example

Collapse

This example shows how to collapse repeated log messages.

What it demonstrates

• LogmeD_Collapse(...) / LogmeD_CollapseIgnore(...)
• LogmeI_Collapse(...) / LogmeI_CollapseIgnore(...)
• LogmeW_Collapse(...) / LogmeW_CollapseIgnore(...)
• LogmeE_Collapse(...) / LogmeE_CollapseIgnore(...)
• LogmeC_Collapse(...) / LogmeC_CollapseIgnore(...)

Notes

• LogmeX_Collapse(limit, ...) uses the formatted message text as the repeat key.
• LogmeX_CollapseIgnore(ignoreRegex, limit, ...) removes all substrings matching ignoreRegex from the formatted message before comparing it with the previous message.
• LogmeX_CollapseIgnore(...) is intended for volatile fields such as request IDs, correlation IDs, timestamps, or counters.
• LogmeX_CollapseIgnore(...) prints the original formatted message. The regular expression is used only for comparison.
• X is one of the usual log levels: D, I, W, E, or C.
• The first message is printed immediately.
• Repeated messages from the same macro call site are skipped until the repeat counter reaches limit.
• Other log messages written by other source lines do not reset that call site's counter.
• The example intentionally writes a normal LogmeI(...) message between calls to LogmeW_Collapse(...) to show this behavior.
• When the limit is reached, logme prints one message with the repeat counter and then starts counting again.
• The limit is count-based, not time-based.
• logme does not currently print a final summary for pending suppressed repeats when the log is closed.

Repeated sequences and multi-line messages

Collapse works on one formatted message at one macro call site. It does not automatically detect that several different log records form a repeated block.

For a repeated sequence such as MQTT Connecting, Connected, Subscribe, and Disconnected, either collapse each log statement separately, or write one diagnostic message containing embedded \n characters if the whole sequence should be treated as one block.

For messages with changing ids, use _CollapseIgnore to remove the volatile part from the comparison key:

LogmeI_CollapseIgnore(
  R"(\[mqtt [0-9]+\])"
  , 20
  , "[mqtt %llu] Connecting to MQTT broker"
  , mqttId
);

Console output

2026-06-10 14:51:40:170 W SameText(): network error: connection refused
2026-06-10 14:51:40:170   SameText(): retry loop is still active, attempt 0
2026-06-10 14:51:40:170   SameText(): retry loop is still active, attempt 1
2026-06-10 14:51:40:170   SameText(): retry loop is still active, attempt 2
2026-06-10 14:51:40:170 W SameText(): repeated 3 times: network error: connection refused
2026-06-10 14:51:40:170   SameText(): retry loop is still active, attempt 3
2026-06-10 14:51:40:170 E Error: IgnoreCorrelationId(): request failed: correlation-id=0, network error: connection refused
2026-06-10 14:51:40:170 E Error: IgnoreCorrelationId(): repeated 2 times: request failed: correlation-id=2, network error: connection refused

Source code

Sources

Repository folder: examples/Collapse

ExampleCollapse.cpp

Open in repository

#include <Logme/Logme.h>

static void SameText()
{
  for (int i = 0; i < 4; i++)
  {
    LogmeW_Collapse(3, "network error: connection refused");
    LogmeI("retry loop is still active, attempt %d", i);
  }
}

static void IgnoreCorrelationId()
{
  for (int i = 0; i < 3; i++)
  {
    LogmeE_CollapseIgnore(
      "correlation-id=[0-9]+"
      , 2
      , "request failed: correlation-id=%d, network error: connection refused"
      , i
    );
  }
}

int main()
{
  SameText();
  IgnoreCorrelationId();

  return 0;
}

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